CHAPTER III. 



GENERAL CHARACTERS OF VENATION, SURFACE 

 AND TEXTURE OF LEAVES. 



Ribs and veins They are water-pipes and distributors of liquids 

 Supporting system Types of venation Parallel and reticulate 

 venation Pinnate and palmate venation Looped, infra- 

 marginal, arcuate and other sub-types Surface characters 

 Glabrous and hairy leaves Forms of hairs Texture of leaves. 



Attention has already been called to the series of con- 

 ducting pipes and of supporting fibres which run as 

 vascular bundles or strands through the soft tissues of the 

 typical leaf, and which serve on the one hand to conduct 

 fluids from stem to leaf and back again, and, on the other, 

 to keep the collapsable tissues well expanded to the light 

 and air, much as the silk of an umbrella is stretched on 

 the ribs. 



In conformity with this analogy, these vascular and 

 librous strands of the leaf are called ribs and veins, and 

 although the latter term is not free from objection, since 

 it would seem to imply that the vascular tubes convey a 

 circulating fluid like that of the blood in animals which 

 is emphatically not the case, because the watery liquids 

 contained in the leaves are very different in origin, con- 

 stitution, movements and functions the inexplicable 



